The present invention is directed an optical device which is utilized in conjunction with a slit lamp biomicroscope, when the biomicroscope is used for indirect ophthalmoscopy or other examination procedures, so as to obtain desired optical characteristics by modifying the illuminating light beam emitted from the projecting lens of the slit lamp biomicroscope. More particularly, the invention is directed to an optical device which may be simply positioned and retained on a conventional state-of-the-art slit lamp biomicroscope in association with the projecting lens thereof to modify the illuminating light beam by filtering, enlarging or otherwise modifying the beam.
The slit lamp biomicroscope has long been utilized as a tool for ophthalmic examinations such as indirect ophthalmoscopy, gonioscopy, fundoscopy or the like. Various forms of slit lamp biomicroscopes have been developed such as the Haag-Streit slit lamps or the Zeiss slit lamps, which essentially achieve similar desired characteristics in the biomicroscope, but have been designed somewhat differently. Conventionally, the slit lamp biomicroscope includes a microscope head, an illumination system producing a slit beam which may be rotated or tilted by the user, as well as patient support structure to facilitate a proper and comfortable examination. In particular, the illumination system of the slit lamp biomicroscope varies with manufacturing designs, but in most cases will allow the slit light beam to be rotated 90.degree. from vertical and may also allow the light path to be inclinable by an angle ranging between 0.degree. and 20.degree.. The entire illumination assembly may be tilted to provide these characteristics or tilting may be accomplished by a rotatory prism or tilting mirror structure. The beam size is also adjustable from an extremely narrow slit to several millimeters in width, and the height of the slit may be controlled by a variable size aperture or diaphragm structure.
Using a slit lamp biomicroscope, observation of particular aspects of the examined eye may be enhanced by only transmitting particular portions of the light spectrum found in the illuminating light beam from the slit lamp light source. Various state-of-the-art slit lamp biomicroscopes have recently included built-in color filters to allow enhanced observation of different aspects of the examined eye. For example, a red filter may be utilized so as to better enable observation of blood vessels on the fundus of the eye. Although various filters have been built in slit lamp biomicroscopes, other desirable characteristics have not been built in to the biomicroscopes and therefore are not available for use during various examination techniques. Similarly, many slit lamp biomicroscopes are not provided with any filtering apparatus at all, or may only include several of the possible desired filters.
Under many circumstances, an indirect ophthalmoscopy lens device is used for examination of a patient, wherein the illuminating light beam from the slit lamp biomicroscope light source is directed through the indirect ophthalmoscopy lens which is held adjacent to the patient's eye. In use with an indirect ophthalmoscopy lens, the maximum possible size of the illuminating light beam reaching the indirect ophthalmoscopy lens is no more than 12 mm in diameter for state-of-the-art biomicroscopes. The indirect ophthalmoscopy lens itself may be of relatively large diameter, and it would be desirable to enable eliminating light beam from the slit lamp light source to fully illuminate the indirect ophthalmoscopy lens for full illumination of the examined eye.